Dog aggressive with postwoman

My springer has just lunged at postwoman. I had the back door open unloading shop from car, and she opened gate and he barked and snarled at her. Luckily no contact was made, not even sure he would bite but you cannot take risk. He always goes mental and barks at door whenever any posts anything.

So I'm straight to shop this afternoon to get a mailbox to put on outside of gate. I feel so guilty

The post person is a big flash point everyday they could and shove stuff into your dog's territory effectively invading it from your dog's point of view. I am afraid I don't have an answer, just an explaination. I do know one postie who pops a dog biscuit through before the post at every house with a dog and now all the dogs love him.

Can't give you a solution. We don't have an enclosed front garden so the dog is never in the garden when post arrives, however we do have a "cage" on the inside of the front door to catch to post as dog goes mad every time and tries to eat/shred the letter! If we are out walking (dog on lead) and the dog see the postman he always tries to pull on lead & bark!